In wellbore drilling operations, information regarding subterranean formations and the position of the bottomhole assembly (“BHA”) are often needed to drill the wellbore in an efficient and cost-effective manner. Thus, in many wells the bottomhole assembly is equipped with an electromagnetic measurement-while-drilling (“MWD”) telemetry tools. These MWD tools provide a current through the surrounding formation and via telemetry circuitry provide telemetry information regarding the BHA. This information is vital to control the trajectory of the wellbore and to successfully position the wellbore relative to desired reservoir formations.
In addition to telemetry information it is often necessary to have formation information available so as to accurately position the wellbore. In practice, a logging tool, such as a resistivity tool is run into the wellbore to obtain information useful to identify particular formation. Currently the resistivity information is obtained by running a separate logging tool into the wellbore to obtain the desired information. Conducting logging operations separate from the drilling operation significantly increases the cost of the drilling operations. The extra expense is justified in some situations. However, in other situations the costs are not justified and the operator is left with controlling the trajectory of the wellbore on limited formation information.
Therefore, it is a desire to provide a formation resistivity measurement into an electromagnetic telemetry tool.